1. Field of Invention
This invention relates to surfacing for wear resistance, specifically to surfacing with a material that also protects the underlying article from corrosion.
2. Description of Prior Art
Aluminum or zinc, when coated onto steel, by the hot dip methods or thermal spray methods, provide a barrier coating that protects steel from corrosion by isolating the steel from the corrosion environment, and also by the cathodic protection principle, whereas, the coating sacrifices itself to protect the steel. Painting is the more familiar method of protecting steel from corrosion through the barrier principle. Hot dip galvanizing is the more familiar method of protecting steel through the use of both the barrier principle and cathodic protection principle. Hot dip aluminizing is another method of protecting steel through the use of both corrosion protection principles. Thermal spraying solid wires or powder is also another familiar method of thermally applying zinc or aluminum onto steel to achieve the two principles of corrosion protection. The barrier principle is simply the process of coating steel with a material that isolates it from the corrosive environment. The cathodic protection principle, performs when the coating has an electromotive potentials more negative than the underlying article, allowing the underlying article to become the cathode and the coating being the anode, when they are exposed to an electrolyte, (corrosive media), the coating will be preferentially attacked thereby protecting the substrate from corrosion. Coatings of zinc or aluminum, or zinc aluminum alloys, being of lower potential than steel, are known to perform this function, and protect steel from corrosion. Other material such as stainless steel or nickel alloys are more positive than steel in the electromotive series, so steel becomes the sacrificial anode when they are coupled. Using the more noble materials as a coating can provide protection to steel by the barrier principle, but will not provide cathodic protection to the steel. Thermally applied Zinc and aluminum coatings, by the before mentioned processes, provide coatings with good corrosion resistance but lack good wear resistance properties.
A solid wire containing a mixture of aluminum and wear resistant particles is manufactured by Alcotech Inc. Traverse City, Mich., for forming a wear resistant coating. This solid wire is limited to a small amount of wear resistant material that can be added, with 10% by volume or less addition, with additions of more than 10% by volume the resultant materials mixture becomes very brittle and cannot be worked, or drawn into a wire or is too brittle to feed with a wire feed process.
A solid wire made of zinc and around 15% by weight of aluminum is manufactured by Platt Brother & Co., Waterbury Conn., for use with the thermal spray processes. The manufacturing of this material is difficult in that aluminum and zinc tend to separate during the manufacturing process, and therefore the coating applied with this material is also inconsistent with patches of pure zinc and pure aluminum, and thus not achieving the full corrosion protection potential of this coating process.
Non slip coatings, are known to be applied, by the electric arc thermal spray process, using filled hollow wires, the use of such wire is shown in U.S. Pat. No. 4,961,973, dated October 1990, W. S. Molnar. This patent does not cite the use of zinc or aluminum for the hollow wire (outer sheath), and did not intend to protect the underlying article from corrosion. The hollow cored wire materials cited in this patent are iron based and will not provide cathodic protection to the substrate, the coating itself will quickly rust and deteriorate when exposed to a corrosive environment. This patent does not consider applications to aluminum substrates, because the iron portion of this filled hollow wire would not provide a suitable metallurgical match for aluminum. The coating would become the anode with the aluminum substrate being the cathode, with this couple, delaminating would soon occur, between the iron base coating and the aluminum substrate.
The thermal methods used to melt and deposit the materials of the present invention are of prior art technology, of the available methods, the most commonly used, are the arc wire thermal spray, flame wire thermal spray, gas metal arc welding, and gas tungsten arc welding. The arc wire thermal spray and flame wire thermal spray methods of applying a coating adheres primarily mechanical to the surface with negligible alloying between the coating and surface of the substrate being coated. The arc wire thermal spray method feeds two wires into respective contact tips that pass electrical current into the wires. The tips are oriented toward each other so the wires extend toward an intersection. A high power is applied across the wires causing an electrical arc to form across the tips of the wires. The electrical current then melts the feed wire portion in the arc zone. A nozzle is located adjacent to the contact tips and oriented to emit an air stream toward the arc zone. The air stream sprays the molten metal onto the work surface forming a coating. The flame wire thermal spray method is similar to arc spray in that it creates a stream of molten metal in a spray form. This method uses one wire and the thermal heat source being of fuel and oxygen. The gas metal arc and gas tungsten arc welding methods melt the surface of the article being coated together with the filler wire to form an alloy of the two materials The gas metal arc welding method uses an electric current as the heat source. A wire goes through a contact tip whereas current is transferred through the wire, and the wire becomes a consumable electrode. The base material is grounded such that an arc is established between the consumable electrode wire and the work surface, as heat is generated by the electric arc, the continuously moving wire and work surface of the base metal melt to form an alloy. The gas tungsten arc welding method is similar in that an electric arc melts the surface of the article being coated. The exception being, the electric arc is established between the base material and a non-consumable electrode held by the welding torch. The work surface of the base material melts and then a filler material is added, in wire or powder form, into the molten puddle. The filler material and base material combine to form an alloy.